Device for heating pieces of work by means of high-frequency alternating currents



Jan. 9, 1951 H. J. M. VAN EMBDEN 2,537,289

DEVICE FOR HEATING PIECES OF WORK BY MEANS OF HIGH-FREQUENCY ALTERNATINGCURRENTS Feb. 7,

Filed H.J. M- VAN EMBDEN v INVENTOR AGENT Patented Jan. 9, 1951 DEVICEFOR HEATING PIECES OF WORK BY MEAN S 01? HiGH-FRE IN G CURRENTS QU @YALTErtNAT- Hendrik .1? ohannes Meerkamp van Embden, Bind hoven,Netherlands, assignor to Hartford Na.- tional Bank and Trust Company,Hartford,

001111., as trustee Application February 7, 1947, Serial No. 727,030 Inthe Netherlands April 2.6, 194d Section 1, Public Law 690, August 8,1946 Patent expires April 26, 1964 1 Claim.

The invention relates to high-frequency induction heating apparatus.

The known devices for heating metal pieces of work by means ofhigh-frequency alternating currents for the thermal treatment of piecesor work comprise a coil for conducting the high-frequency alternatingcurrents. In the space inside this coil there is produced ahigh-frequency alternating field by which the outer layer of the pieceof work brought into this field is heated through induction of Foucaultcurrents. The efficiency of such a device is highly dependent on thatportion of the magnetic alternating field produc'ed in the coil which isused efficiently for the production of Foucault currents in the piece ofwork, that is to say on the part of the field which crosses this pieceof work. As a rule, the coil will have much larger dimensions than thepiece of work introduced, since in view of the high voltages to be usedit is desirable that the dimensions of the coil and the distance betweenits turns should be such that in many cases the coil is necessarily ofan excessive size. A great portion of the magnetic field produced willtherefore not pass through the piece of work. In order to overcome thisdrawback, it is already known to use flexible turns for the coilproducing the highfrequency field, so that these turns may be adapted topieces of work of difierent shapes. There are, however, objections fromthe point of View of construction, since these turns generally have toconduct comparatively strong currents and mostly have to be cooled by awater current.

A known solution to meet the above-mentioned drawback of the dimensionsof the coil relative to the piece of work while retaining acomparatively large coil consists in the provision of a filling piece ofnon-magnetic material having a high electrical conductivity between thecoil and the piece of work concerned. Such known filling pieces consistof brass or copper bodies provided with a central aperture whichcommunicates with the outer periphery by means of a slot. The Foucaultcurrents produced in this conductive body by the high-frequencyalternating field fiow, owing to the wall effect in the externalperiphery of the body, along the area of the slit and along the internalperiphery of the central aperture recessed in the said body. In thecentral aperture there is thus produced again a high-frequencyalternating field in which is located the piece of work to be heated. Itis thus possible to treat efiiciently also small pieces of work whileretaining a coil of the required dimensions, since the aperture of thefilling piece may be adapted to the piece of work. The filling pieceacts in this case as a secondary Of a transformer whose primary isformed by the coil. These known conductive bodies have the drawback,however, that for heating pieces of work in which small diameters aswell as large diameters occur, the parts with small dimensions may beintroduced only if the slot communicating with the external peripheryhas a width equal to at least this diameter.- The piece of work to beheated is therefore during the heating in the central aperturenot in thealternating field throughout its section. It is possible indeed to givethis slot a'small width, but in this case it must always be possible topass the whole piece of work through the central aperture, which cannotbe realised, for example, in the case of crank-shafts and similarcomplicated pieces of work without giving the central aperture too greata width and hence rendering the body too little effective.

These drawbacks are obviated by the present invention, in an arrangementwherein the conductive body is built up from at least two differentparts and the piece of work is located in a portion of the intermediatespace between the separate parts. Owing to this measure it is ensuredthat the conductive body concerned may be opened before the introductionand the removal of the piece of work, so that small diameters of piecesof work may also be surrounded by the conductive body at a smalldistance therefrom.

In the construction according to the invention care is preferably takenthat at least part of the inner surface of the conductive body dividedinto parts has such a shape and such dimensions that this surface isadapted to the total part of the piece of work that is to be heated.This exact adaptation has the advantage of a minimum leakage field.

In order that the invention may be more clearly understood and readilycarried into effect, it will be explained more fully by reference to theaccompanying drawing.

Figures 1 and 2 give a plan view and a sectional side view of the deviceaccording to the invention.

In Figure 1, the coil 1 contains a body which is constituted by twoparts 2 and 3 which parts may be cooled, said body consisting ofnon-magnetic material of good electrical conductivity, for example ofcopper.

A high frequency alternating field is produced in the coil I. When thecurrent in the coil flows in the direction of the outer arrows, Foucaultcurrents are produced in the parts 2 and 3, which flow in accordancewith the indicated arrows owing to the edge efiect. The piece of Workwhich must be externally hardened is located in the aperture 4 betweenthe two pieces 2 and 3, about which also flows a high-frequencyalternating current, as can be seen from the drawing.

Fig. 2 is a sectional view of a device according to the invention. Asbefore, I is the coil traversed by the high-frequency alternatingcurrent. The parts 2 and 3, which in this case are provided withinclined holes 5 and 6, embrace the aperture 4 which can exactly receivethe piece of work I, in the present instance a part of a balljoint. Thepart 8 of this piece of work need not be hardened and is thereforelocated outside the space 4. As a result of the inclined holes 5 and 6,the current flowing directly about the piece of work is concentratedstill further, from which a quicker heating results.

The two parts 2 and 3 are supported by limbs 9 and ill, the piece ofWorkbearing on a support II. If desired, the piece of work may berotatably arranged to facilitate a more uniform heating thereof. Thewhole is fastened on a carrier l 2 which may be moved up and down alongthe longitudinal axis of the coil. For exchanging the piece of work thecarrier I2 may be lowered and the parts 2 and 3 may be turned away roundthe limbs 9 and [0. Owing to this possibilityof movement of the parts 2and 3 the additional advantage is obtained that the opening 4 may beadapted to the piece of work better than with the known devices having afilling piece.

-. What I claim is:

High-frequency induction heating apparatus for treating work piecescomprising a solenoid for establishing a high-frequency field, anonmagnetic cylindrical body of metallic material of high electricalconductivity coaxially disposed within said solenoid, said body beingconstituted by a pair of spaced longitudinal segments, the work piece tobe treated being disposed in the spacing between said segments, theinner surfaces of said segments being shaped to conform substantially tothe contour of said work piece, whereby eddy currents induced in saidsegments results in a flux field threading through said work piece, anda carrier movable relative to the solenoid along the longitudinal axisthereof for holding said workpiece in the spacing between said segments,said carrier including means pivotally supporting said segments toenable insertion and removal of said work piece.

HENDRIK JQOHANNESI MEERKAMP vm, EMBDEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Num er Name Date 1,997,741 Northrup Apr. 16, 19352,299,934 Sherman et al Oct.27, 1942 2,408,229 Roberds Sept. 24, 19462,442,968 Bierwirth June 8, 1948

